Examples of related biometric authentication devices are disclosed in a patent document 1, a patent document 2, and a non-patent document 1.
Biometric authentication systems of these types include, as shown in FIG. 3 of the patent document 1, an externally-supplied sound determination unit, an externally-supplied sound synthesizing unit, a bone conduction speaker, a bone conduction microphone, a feature amount extraction unit, a feature amount collation unit, and a feature amount database.
A biometric authentication system having such a configuration operates as follows. A biometric authentication system determines externally-supplied sound that is supplied from outside of a person to be authenticated by the externally-supplied sound determination unit, synthesizes the externally-supplied sound based on the determined externally-supplied sound, and transmits the synthesized sound to the bone conduction speaker. The signal transmitted from the bone conduction speaker is received by the bone conduction microphone through a human body (skeleton) of the person to be authenticated who contacts the system. The biometric authentication system extracts the personal feature by performing frequency analysis of the bone conduction sound in the feature extraction unit from the received signal, and performs collation with personal data which is enrolled in the feature amount database by the feature amount collation unit, so as to perform personal authentication.
Further, a biometric authentication device disclosed in the patent document 2 includes a pulse generation unit, a speaker, a data synthesis unit, a microphone, a template storing unit, and a comparative determination processing unit. The pulse generation unit generates a pulse, and irradiates a finger of the person to be authenticated contacted to the speaker with a signal that is amplified by an amplifier. The biometric authentication device receives an impulse signal transmitted through living body tissue of the finger by the microphone. The data synthesis unit synthesizes the pulse generated by the pulse generation unit and the impulse received by the microphone. The biometric authentication device stores synthesized synthetic wave in the template storing unit as personal identification information of the person to be authenticated. The biometric authentication device generates a synthetic wave in authentication in the same way as enrollment, calculates the mean square value of the difference of the template by the comparative determination processing unit, and performs personal identification processing by the threshold processing of the mean square value.
Meanwhile, the non-patent document 1 suggests a method of carrying out biometric authentication using an ear canal (earhole). This method observes a response signal of an acoustic signal transmitted to the ear canal with a speaker by a microphone that does not directly contact to the living body, and obtains a transfer function of a signal in the ear canal by Fourier transformation from the acoustic signal and the response signal. In this method, personal identification is performed using linear discriminant analysis for this transfer function.    [Patent document 1]    Japanese Unexamined Patent Application Publication No. 2003-58190    [Patent document 2]    Japanese Unexamined Patent Application Publication No. 2003-248664    [Non-patent document 1]    A. H. M. Akkermans, T. A. M. Kevenaar, D. W. E. Schobben, titled “Acoustic Ear Recognition for Personal Identification”, (U.S.A), Fourth IEEE Workshop on Automatic Identification Advanced Technologies (AutoID'05)), 2005, p. 219-223